Cannot figure out how the Transform.CreateRotationAtPoint() works! Help

[Anonymous]

I am trying to take an XYZ point and rotate it 1Pi (180 degrees) around another base point. I think I got the correct method but I cannot figure out how to use it. See image attached

Base point = XYZ Origin? Is the base point considered the origin? I think so...

How do I define the AXIS using an XYZ? Does anyone have an image to explain this? I couldn't find any documentation. I want to rotate the point along the XY plane (in plan orientation).

The angle is in Radians, I got that one.

Transform transf = Transform.CreateRotationAtPoint(new XYZ(Origin.X,Origin.Y,Origin.Z +1), Math.Pi, Origin);

transf.whatMethodHereToGetNewXYZLocationOfPoint?

Once I get the transform, how do I get the new XYZ location of my rotated point?

thanks.

[jeremytammik]

Dear Redsky,

Transform.CreateRotation

creates a rotation transformation given just two arguments, the rotation axis and angle.

CreateRotationAtPoint takes three arguments: the axis, rotation angle and base point.

Here is one short description of how not to use CreateRotationAtPoint  🙂

http://thebuildingcoder.typepad.com/blog/2014/02/different-revit-api-aspects-and-features.html#5.2

To define an axis by an XYZ, simply cnsider the XYZ a vector instead of a point.

In your case, to determine the rotation of the point pOld to the result pNew by 180 degrees around the base point base_point in the XY plane, i.e., around the Z axis, you can do this:

  XYZ axis = XYZ.BasisZ;
  double angle = Math.PI;
  Transform t = Transform.CreateRotationAtPoint(
    axis, angle, base_point );
  XYZ pNew = t.OfPoint( pOld );

Cheers,

Jeremy

[jeremytammik · Accepted solution]

Added it to The Building Coder:

http://thebuildingcoder.typepad.com/blog/2015/06/create-duct-pipe-and-point-transform.html#3

Cheers,

Jeremy